This project deals with the genetic and biochemical bases of chemotactic behavior in the simple bacterium, Escherichia coli. The major aims are: (1) to determine the complexity of the chemotaxis machinery; (2) to analyze the pathways of information flow from chemosensors to flagella; (3) to investigate the nature of signalling and stimulus transduction events in this system. Toward these ends, a number of generally nonchemotactic mutants have been isolated and characterized both genetically and physiologically. The mutants define 8 genes whose products are involved in generating or regulating reversals in the direction of flagellar rotation. Specialized lambda transducing phages carrying some of these genes are being constructed for further genetic and biochemical studies. Reversion analyses show that many of the gene products interact with one another or with components of the flagellar basal body. From information of this sort, it has been possible to assign specific roles to most of the gene products. BIBLIOGRAPHIC REFERENCES: Hazelbauer, G. L. and Parkinson, J. S. "Bacterial Chemotaxis" in Receptors and Recognition: Microbial Interactions, J. Reissig, ed. Chapman and Mall, London, 1977, in press. Parkinson, J. S. "Behavior Genetics of Bacteria." Ann. Rev. Genetics, 1977, in press.